docs: def get_climatology_variable(ds):
      '''
      Returns the variable describing climatology bounds if it exists.
  
      Climatology variables are similar to cell boundary variables that describe
      the climatology bounds.
  
      See Example 7.8 in CF 1.6
  
      :param netCDF4.Dataset ds: An open netCDF4 Dataset
      :rtype: str or None
      '''
      time = get_time_variable(ds)
      # If there's no time dimension there's no climatology bounds
      if not time:
          return None
      # Climatology variable is simply whatever time points to under the
      # `climatology` attribute.
      if hasattr(ds.variables[time], 'climatology'):
          if ds.variables[time].climatology in ds.variables:
              return ds.variables[time].climatology
      return None